Interaction of Surfactants and Heterogeneous Systems
Let’s define a heterogeneous system of oil and water. (System 1)
If we expose system 1 to a surfactant, the tensioactive will immediately place itself in the region of the interphase, decreasing the surface tension of the boundary. (System 2)
If we apply enough energy (i.e. shaking) to system 2, we will form an emulsion. The microscopic view of such an emulsion is the micelle:
Image: the Green Chemistry=Dream Chemistry gallery
The micelle will contain the lipophilic substances in its interior leaving the hydrophilic section of the surfactant’s molecule to interact with the water.
The Cleaning Process
We covered all concepts necessary to understand, at a molecular level, the mechanism of action of the cleaning process. Now we will describe the model that has been around for at least a century. After that we will propose an evolution of the old model that should be applied to biological systems, such as hair.
Even though undesired substances on a surface could be hydrophilic or lipophilic, since the lipophobic ones can be removed with plain water, they are never a subject of study when researching detergents and surfactants in general. So, throughout this paper, we will refer to lipophilic dirt.
Following what we learned so far, we know that the reason dirt cannot be removed with water alone is because water will not “wet” the dirt, and the lipophilic substance will not tranfer to the solvent. Water will not wet dirt because its surface potential is higher than the solid phase, thus there is a very high surface tension in the system.
As we explained before, we need to decrease the surface tension to increase wettability and get the surface clean. To decrease the surface tension, we must use a surfactant or tensioactive solution with the water. Here is how the traditional model looks in a diagram (non-biological system):
Logically, when detergents are formulated they are meant to remove EVERYTHING from the surface, so they do not discriminate among different superficial potentials and superficial tensions. The reader will be able to find literature about different types of detergents, like the Alkylic Carboxylated Ethers or the Mg detergents, that are gentler and more skin compatible.
Although gentler, they do not have the chemical ability to be selective. The requirement of using conditioner after washing is a demonstration of this. Hair is a biological heterogeneous system with plenty of components; for the benefit of the discussion of the model to follow, we will simplify it to a system of 3 degrees of freedom.
While hair is mainly made of proteins with a certain amount of S- Bridges (the number of Sulphur bridges will define the amount and size of the curls), sebum is composed of triglycerides, wax esters, squalene and metabolites of fat-producing cells – needless to say, very lipophilic substances. As we established before, the dirt accumulated in hair is mainly composed of substances from the elements and “used” and not-needed sebum. Also, we can infer with a high degree of certainty that in-use sebum will be more strongly linked to the hair than outside substances or sebum that has been discarded by the body.
Using words and concepts mentioned earlier in this paper, the superficial tension between hair and sebum will be higher than the superficial tension between dirt and hair and between dirt and sebum.
All detergents have a very strong amphiphilicity due to their long carbon chain (Lipophilicity) and very strong-to-strong ionic segments in the molecule. Even so-called mild detergents like the Alkylic Carboxylated Ethers have at least 2 O2- with strong negative charges per molecule. That is why all detergents are tensioactive enough to affect even the highest of the superficial tensions of the system, thus removing everything including the benevolent and protective sebum film.
So, the diagram of a hair sebum/dirt system, when exposed to shampoo with ANY detergent will be as follows:
Strong surfactants like detergents and soaps will strip the hair and remove its protection in every wash. This causes dryness and negative feedback to the scalp that overproduces protection (sebum) to compensate. When that happens, the system might suffer a paradox: dry hair ends and an oily scalp.
In a curly hair system, the physiology of the follicles is different. The hair grows at a far more acute angle, and the shape and texture of the hair itself makes dryness more severe and longer lasting than with less textured hair. Dryness creates the perfect condition for static, like the Pink Panther inserting a finger in a power outlet. Conditioner and other “repairing” products are normally used to mask the harm that shampoo causes.
Instead of breaking and then repairing hair, what if we wash hair without breaking it so we do not need to repair it? If we think it from a scientific point of view, the answer comes easily. We need to find a molecule or a blend of molecules that can decrease the surface tension enough of the sebum/dirt system without modifying the superficial tension of the hair/sebum system to a point that water can remove it. As it happens many times in science, the theoretical answer to a question is an easy one. It gets trickier when one has to bring the theory to reality.
Two aspects of the surfactant can be modified:
• Modify the carbon chain to manage the lipophilic side of the molecule
• Modify the hydrophilic part of it to be strong enough to interact with water when the lipophilic end is interacting with a less linked substance like dirt – but make it weak enough to not be removed by water when the carbon chain interacts with a strongly linked lipophilic substance like sebum.
To do as proposed in the second instance, we need to find a blend of molecules that earn their amphiphilicity with chemical groups like OH-, NH4-, etc. New Wash uses a proprietary blend of fatty alcohols, complex oils and some large molecules with rings and amino groups.
The reference we will use to explain the model is the fatty alcohol in larger presence in the blend: Cetyl Alcohol.
This particular blend is going to work as a selective surfactant, only removing substances that have a surface tension and surface potential lower than the same magnitudes for the hair/sebum system. What makes this blend so effective at cleaning hair without stripping it is also its worst characteristic: to clean effectively and remove excess product, the user must rinse profusely in order to make sure that the weak hydrophilic groups “grab” the water and drag the dirt away.
On the positive side, many molecules in the blend that “link” to the sebum during the wash will stay put on the hair. Since all of them have some moisturizing properties, softened hair will be a very pleasant side effect.
The improved model diagram for biological Systems:
This theoretical model was corroborated empirically with the following experiment conducted by the author of this paper with hairdresser Steven Petersen in Salt Lake City, Utah.
Empirical experiment to demonstrate the selectivity of New Wash and a comparison with highly regarded color preserving shampoos
Detergent-based shampoo has been the go-to product to wash hair for centuries, and the cleaning power of saponified molecules (detergents) is extremely efficient. Human hair is mainly a protein structure, neither irrigated nor enervated, and naturally protected by the secretion of a heavily lipophilic blend of substances by sebaceous glands located very close to the follicle.
When hair is washed with a detergent, this natural protection is removed leaving the hair exposed to the environment. The result is a dry protein formation full of electrostatic charges. Hair care companies solved the problems caused by shampoo/detergent by recommending conditioners and masks to artificially restore moisture.
We set out to prove that the use of a less hydrophilic surfactant than detergents can remove undesired dirt without removing more linked substances like natural sebum. To prove the hypothesis that we can get naturally healthier hair without extra products (conditioners, etc.), we used semi-permanent color to mimic natural sebum.
Materials and Methods
We ran two experiments using natural hair extensions. One, with uncolored extensions tested New Wash’s cleaning power compared with two well-known shampoo (detergent) brands. Each extension was immersed in used motor oil and then double-washed with New Wash, Shampoo 1 and Shampoo 2 respectively.
For the second part of the experiment we used natural hair extensions colored with a premium brand of semi-permanent hair color. These colored extensions were washed 100 times with New Wash and 10 times with the detergent-based shampoo.
The third experiment was to wash the hair of a living person dividing the head in two. One side was washed 10 times with New Wash and the other side was washed 10 times with the most expensive of the color protective shampoos used in the experiment above.
The process of coloring hair opens the quaternary structure of the protein allowing the chromatic molecules to link strongly to hair when that structure is reestablished.
We believe a semi-permanent color product to be a good analogy to sebum. If color remains after washing, then sebum should also remain. We recorded on video, with no edits, the process of washing equally colored natural hair extensions, with two market leader color protective brands of shampoo (with detergent) and with New Wash (without detergent that uses low hydrophilic surfactants as cleansing agents).
As seen below, the results with the two groups of products (with and without detergent) were surprisingly different to the naked eye. In the experiment with the extensions we can see that New Wash kept the color almost intact even after 100 washes, while the shampoos with detergent had a clear loss of color even after only 10 washes.
In experiment three, we can see similar results. We must say that in the first experiment, where we washed an extension immersed in used motor oil, the cleaning results were comparable for New Wash and the detergent-based shampoo. The only difference was the need to rinse about twice as long with New Wash than with the detergent-based shampoos.
Left: Starting color for all experiments. Center: After 10 washes with New Wash (left) and Shampoos with detergent (center and right). Right: Control with no washes (left); after 10 washes with New Wash (center left); after 100 washes with New Wash (center right); after 10 washes with the most expensive of the shampoos with detergent (right).
Left: Before washing; Center: Washing with shampoo (left), New Wash (right); Right: New Wash (left), shampoo (right)
In all cases we see a very clear difference in the results after the interaction of the extensions with the cleansing products. All shampoos with detergent removed a significant amount of color in less than 10 washes (in the video footage it is very clear that at least 40% of the color is lost in the first wash). In contrast, New Wash instead preserves the color even after 100 washes.
These results are a clear indication that a less hydrophilic surfactant can work in a more selective way, removing only the undesired deposited substances (dirt) and preserving the more linked hair protection (sebum). Shampoos with detergent are not selective and they remove both desired and undesired substances. This leaves the hair unprotected and in need of hair conditioner and other remedies to undo the stripping caused by the detergent present in shampoos.
All original and unedited video footage is on file with the author.